JPS62104497A - Driving circuit for step motor - Google Patents

Abstract

PURPOSE:To make the coil current of a step motor zero by giving a predetermined positive offset voltage to the input of a voltage comparator and by reducing the reference voltage value of the voltage comparator below the DC offset voltage. CONSTITUTION:Regardless of the current value of a coil 16 a DC offset voltage is optionally given to the inversion input terminal of a voltage comparator 2 by the partial pressure ratio between a resistance 20 and a resistance 21. It is possible to make the current of the coil 16 completely zero, so long as the reference voltage value, which is inputted to the non-inversion input terminal of the voltage comparator 2 where a DC offset voltage is given, is reduced more than that of the equation as shown above the figure. (in which R20 and R21 denote the resistance values of the resistances 20 and 21 respectively. while Vcc denotes the voltage of source.)

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a step motor drive circuit, and particularly to a constant current control type step motor drive circuit.

[Summary of the invention]

The present invention provides a constant current control type step motor drive circuit powered by a single power source, which includes a first resistor that detects the current flowing through the coils of each phase of the step motor, and a voltage generated in this resistor. A second resistor is inserted between the receiver and the voltage comparator, and a third I+ (resistance is
1, a certain DC offset voltage is applied to the input of the voltage comparator by the voltage division ratio of the second resistor and the third resistor, and the reference voltage of the voltage comparator is changed. This makes it possible to vary the current flowing through the coil.

[Conventional technology]

FIG. 2 shows an outline of a conventional constant current control type step motor drive circuit. FIG. 2 shows only one phase of the two-phase bipolar motor drive circuit, and since the circuits for the other one phase are completely the same, they will be omitted.

The coil (S) of the step motor is connected to the current control transistor (J) and (L) or (S) from a single power supply (1)).
Current (j (supplied) through and (nu).

All currents flowing into the coil (1) pass through the current detection resistor (1) and flow to the ground terminal. The Δ output of the step motor controller]・r”−ra(・i) is the coil (
1-transistor (H) for controlling the current direction of (DELTA high and high level human output)
1) is turned on, and a current flows in the direction of the arrow 101 in the 2nd Ill (S). When the A output is at a low level, the current control transistors (S) and (N) are turned on, and the current control transistors (S) and (N) of the coil (S) are turned on.
The flow direction is in the direction of arrow 102. The current flowing through the coil (S) flows through the current detection resistor (R), and that resistance (Y)
The voltage generated at is input to the inverting input terminal of the voltage comparator (b). When the voltage value generated on the current detection resistor (Y) exceeds the reference voltage value input to the negative input terminal of the voltage comparator (B), the output of the voltage comparator (B) changes from high level to low level. , operate with a single-shot signal generator, inhibit the AND circuit (to), ()) for a certain period of time, and turn on the current control transistor (nu).

(l) is turned off.

Therefore, the reference voltage input to the non-inverting terminal of the voltage comparator (B) determines the value of the current flowing through the coil (S) of the step motor, and the coil (S) is driven at a constant current.

[Problems and objects to be solved by the invention] As described above, in the prior art described above, the coil current value of the step motor is changed by changing the reference voltage value of the voltage comparator. be. The need to vary the coil current arises when the step motor is precisely positioned by the step drive of the microphone 11. In the case of a two-phase bipolar motor (because positioning is performed finely using microstep drive), the current value of each phase must be changed independently from zero to the maximum current. The problem is when you want to make the current value zero.It seems that in order to make the 1F current value zero, you just need to make the reference voltage value of the voltage comparator zero, but in reality, this is not the case. This is because there is always an input offset voltage at the input of the voltage comparator, and the input offset voltage can be both positive and negative.Therefore, the offset voltage causes the non-inverting input terminal of the voltage comparator to If the reference voltage input to the non-inverting input terminal is higher than that of the inverting input terminal, it is impossible to reduce the coil current to zero unless the reference voltage input to the non-inverting input terminal is set to a negative voltage lower than that of the ground terminal.

Therefore, in order to reduce the coil current in the prior art, it was necessary to adjust the offset voltage of the voltage comparator or to prepare a negative power supply for the reference voltage. Adjusting the offset voltage increased assembly man-hours, resulting in a significant cost increase. Furthermore, if a semi-fixed resistor or the like was used for adjustment, reliability would be significantly reduced due to changes in contact resistance. Furthermore, providing a negative voltage for the reference voltage imposes an extreme burden on the circuit in products whose power supply voltage specifications are fixed.

Therefore, the present invention aims to solve these problems.
The purpose of this is to create a constant current control type step motor that allows for inexpensive, stable, micro-step drive by making it possible to change the coil current value of the step motor from zero without any adjustment and without the need for a negative power supply. It provides a motor drive circuit.

[Failure to solve the problem]

A transistor that controls the current flowing through the coils of each phase of the step motor, and a first transistor that detects the current flowing through the coils.
a resistor, a voltage comparator that receives the voltage generated in this resistor, a single-shot signal stopper that receives the output of this voltage comparator and generates a pulse for a certain period of time, and an output signal and step of this single-shot signal generator. It is equipped with an LJ that receives the phase signal of the motor, an AND circuit that drives the transistor of the corresponding phase by its output, and a surge voltage absorption circuit that protects the transistor from the surge voltage generated in the coil, and is powered by a single power supply. In a step motor drive circuit that can change the current value flowing through the coil by changing the reference voltage of the voltage comparator, the step motor drive circuit includes the first resistor for detecting the coil current, and the resistor. By inserting a second resistor between the voltage comparator that receives the generated voltage, and by adding a third resistor between the connection point of the second resistor and the voltage comparator and the power supply. , the base Y1 of the voltage comparator! The present invention is characterized in that the current flowing through the coil can be changed from zero by changing the voltage.

[Effect]

According to the above configuration of the present invention, the second resistor is inserted between the first resistor that detects the current flowing in the coil of the step motor and the voltage comparator, and the second resistor is further inserted between the second JIE resistor and the voltage comparator. By inserting a third resistor between the connection point of A certain positive DC offset voltage is applied to the input of the voltage comparator by the voltage division ratio of the third resistor, and the reference voltage value of the voltage comparator is lowered by lowering the DC offset voltage. It is possible to reduce the current to zero.

〔Example〕

FIG. 1 shows an outline of an embodiment of a constant current control type step motor drive circuit of the present invention. FIG. 1 shows only one phase of the two-phase bipolar motor drive circuit, and since the other one-phase circuits are completely the same, they will be omitted.

The step motor coil 16 is powered by current transistors 8 and 11 from a single power supply 17. Or current is supplied via 9 and 10. All current flowing into the coil 16 flows to the ground terminal through the current detection resistor 18. The A output of the step motor controller 1 is a signal that controls the direction of the current flowing to the coil 1. When the turnout J is at a high level, the current control transistor 8.11 is turned on, and the current direction of the coil 16 is indicated by the arrow 201. A current flows through. When the output to is at a low level, the current control transistor 9.10 turns on, and the coil 16
The current direction is in the direction of arrow 202.

The current flowing through the coil 6 flows through the current detection resistor 18,
A voltage is generated across the resistor 18.

The above configuration and operation are completely the same as the conventional technology.

Further, the diodes 12, 13, 14, and 15 form a surge voltage absorption circuit that absorbs the surge voltage generated in the coil 16 when each transistor is turned off. The voltage generated across the current detection resistor 18 is input to the inverting input terminal of the voltage comparator 2 via the resistor 21. Further, a resistor 20 is connected between the inverting input terminal of the voltage comparator 2 and the power supply I7.

Here, the voltage 'tA17 is set to VCC, the resistor 18 is set to R18, the resistor 20 is set to R20, the resistor 21 is set to R21, and the current of the coil 16 is set to 18. The input offset voltage of voltage comparator 2 is V. F a,
, and the inverting input terminal voltage of voltage comparator 2 is V raf
If we set it as t, the following formula holds true.

RIB-LH) ±V OFT Therefore, when the coil current I is zero, the equation is as follows.

Here, set the following conditions.

Therefore, the inverting input terminal of voltage comparator 2 has coil I6.
Regardless of the current value, it is possible to arbitrarily apply a DC offset voltage by adjusting the voltage division ratio between the resistors 20 and 21.

The reference voltage value input to the non-inverting input terminal of the voltage comparator 2 to which the DC offset voltage is applied is R1O+RZl. Transistor 8. ,
9. 10. 11. A predetermined current flows through it.

When inputted to the non-inverting input terminal of the voltage comparator 2, the output of the voltage comparator 2 becomes a low level, and the single-shot signal generator 3 turns on the coil 16 in order to disable both the current control transistors 10 and 11 for a certain period of time. The current path is closed, and no current (J) flows through the coil 16.
In order to avoid prohibiting 0°II, a high [・bell signal is output, but
After a certain period of time has elapsed, the power is manually applied, but if the level is still low, the same output state continues for a further certain period of time. In this way,
By applying a voltage to the non-inverting input terminal of the voltage comparator 2, it is possible to completely reduce the current in the coil 16 to zero.

Above, the circuit configuration and operating principle have been explained using a two-phase bipolar motor as an example, but other step motors, such as a four-phase unipolar motor.

The present invention can be similarly applied to five-phase bipolar motors and the like.

Further, the reference voltage of the step motor controller 1 connected to the non-inverting input terminal of the voltage comparator 2 is normally generated by a D/A converter in the case of the current drive circuit that performs microstep drive.

〔Effect of the invention〕

As described above, according to the present invention, in a constant current control type step motor drive circuit where power is supplied from a single power source, it is normal to completely reduce the coil current of the step motor to zero. Due to the input offset voltage of the voltage comparator, it is very difficult to adjust the offset voltage or
The need to prepare a negative power supply for the reference voltage is no longer necessary. Adjusting the offset voltage increases the number of assembly steps and causes a large cost increase. Furthermore, if a semi-fixed resistor or the like is used for adjustment, reliability will be significantly lowered due to changes in contact resistance. Furthermore, preparing a negative voltage for the reference voltage is almost impossible for products with fixed power supply voltage specifications, so why not use a negative voltage? ``When preparing voltage, it is necessary to use extremely burdensome circuits such as DC-DC converters, which not only increases costs, but also puts pressure on other parts in the case of products with space constraints. However, according to the present invention, these conventional problems can be eliminated, and the adjustment work can be simplified by simply adding two resistors to the conventional circuit. This eliminates the need for a step motor drive circuit that is low in price, highly reliable, and extremely advantageous for downsizing equipment.

The present invention is applicable to products that require precise positioning using a step motor, such as node disk drive devices, floppy disk drive device positioning, and printers.

Positioning the carriage of a facsimile machine or the X of a sewing machine
, can be applied to Y-axis positioning, etc.

[Brief explanation of drawings]

FIG. 1 is a schematic circuit diagram showing an embodiment of a step motor drive circuit of the present invention. FIG. 2 is a schematic circuit diagram of a conventional step motor drive circuit. 12.13,14,15. (wo), (wa). (Force) (Yo)...Diode 4.5, 19. (D), (E) (T)... Inverter 6.7. (to), ())...AND circuit or more

Claims (1)

[Claims] A transistor that controls the current flowing through the coils of each phase of the step motor, a first resistor that detects the current flowing through the coil, a voltage comparator that receives the voltage generated in this resistor, and a voltage comparator that receives the output of this voltage comparator. a single-shot signal generator that generates a pulse for a certain period of time; an AND circuit that receives the output signal of the single-shot signal generator and the phase signal of the step motor, and drives the transistor of the corresponding phase with its output; It is equipped with a surge voltage absorption circuit for protecting the transistor from the generated surge voltage, is supplied with power from a single power supply, and is capable of changing the value of the current flowing through the coil by changing the reference voltage of the voltage comparator. In the step motor drive circuit that can be used,
A second resistor is inserted between the first resistor that detects the coil current and a voltage comparator that receives the voltage generated in this resistor, and a power source is connected to the connection point between the second resistor and the voltage comparator. A step motor drive circuit characterized in that the current flowing through the coil can be changed from zero by adding a third resistor between the voltage comparator and changing the reference voltage of the voltage comparator.